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October 13, 2017 – In Chengyun Hua’s research, everything revolves around heat and how it moves. As a Russell Fellow at the Department of Energy's Oak Ridge National Laboratory, Hua carefully analyzes nanoscale heat transfer mechanisms using laser spectroscopy.

“Heat is being generated from everywhere and we can collect that heat and convert it to energy,” she explained. “We essentially have enough heat being produced 24/7 through electronics and other sources that we could potentially impact the world’s energy production and ease today’s energy concerns.”

Although heat has the potential to generate enough energy to power the universe, if not channeled properly, it can also become problematic.

“We’ve seen recent news of cell phones bursting into flames,” Hua said. “The reason is too much heat is produced locally, and it has nowhere to go in a short period of time. The challenge is to capture that heat flow at the nanoscale and understand how we can more effectively dissipate it.”

Through Hua’s work in ORNL’s Building Equipment Research group, a new ultrafast optical technique for thermal measurements—time-domain thermoreflectance—was deployed at ORNL for the first time. The technique measures the thermal properties of materials, including thermal conductivity. Using ORNL’s Ultrafast Laser Spectroscopy Laboratory, Hua measures material conductivity down to the nanometer.

“When a material is heated using a pulsed laser, thermal stress is induced,” she explained. “The objective of raising the temperature of a material is to unveil the microscopic processes of the phonons [a type of elementary particle that plays an important role in many of the physical properties of solids, such as the thermal conductivity and the electrical conductivity] that govern the heat transport in solids. Ultimately, with this better understanding, we can design the next generation of materials—materials that not only withstand heat but also manage the heat and convert it into energy.”

For the love of physics

Hua grew up a world away in Shanghai, China. An only child of accountant parents, she excelled in mathematics and science, something that was not unusual in her home country.

“It’s easy to get a job in the engineering discipline in China; it’s a highly respected profession,” she said. For Hua, however, getting accepted to study engineering physics at the University of Michigan, Ann Arbor, was an opportunity not to be missed.

“Studying in Michigan was the first time I had ever been to the United States,” she said. “But it wasn’t until I entered the mechanical engineering program at Cal Tech that I truly felt at home.”

Hua completed her PhD in mechanical engineering at the California Institute of Technology at Pasadena. There she met an advisor and professor who helped steer her current career path, challenging her to continue focusing on nanoscale heat transfer properties. “Cal Tech was a unique playground if you love mathematics and physics,” she said.

After meeting some ORNL researchers at a Society of Women Engineers conference, Hua made the decision in early 2016 to apply for a fellowship that would allow her to focus on micro- and nanoscale heat transfer and energy conversion at the lab. The Liane B. Russell Distinguished Early Career Fellowship attracts scientists who have demonstrated outstanding scientific ability and research interests that align with core capabilities at the lab.

“My advisor encouraged me to apply and within one week I wrote my proposal on ‘Exploring Thermal Transport in Nanostructured Materials for Thermal Energy Conversion and Management.’ I interviewed in November 2015 and four days after the new year, I was invited to become a fellow at ORNL,” she said.

Uprooting again to East Tennessee, Hua has found a supportive community that encourages the sharing of new ideas and interdisciplinary research.

“I’ve been able to live in different parts of the U.S.,” she said. “But, everywhere I’ve been, I’ve found support and an environment that promotes ideas and stimulating conversation between scientists.”

While Hua has adapted to many moves and changes, one part of her research and studies remains unchanged.

“Heat always flows from hot to cold,” she said. “It’s the constant in the continuum.”

ORNL is managed by UT-Battelle for the Department of Energy's Office of Science, the single largest supporter of basic research in the physical sciences in the United States. DOE’s Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov. —Jennifer Burke